There have heretofore been numerous proposals concerning methods of making decisions as to the occurrence of a fire by comprehensively judging data which is available from a plurality of similar or different types of fire detectors or a method of making the fire decision by comprehensively judging all the data produced by individual sensor parts of multi-element fire detectors each incorporating a multiplicity of sensor elements for detecting heat, smoke or gases. For example, as a system or equipment embodying the above method, there is known one in which the fire decision is made when a value resulting from integration or multiplication of individual elementary sensor outputs exceeds a predetermined value. According to another known system, the fire decision is validated when a predetermined value is exceeded by substituting output values of individual sensors in a specific function. Additionally, there is known a method in which a table defining relations between inputs and outputs is previously prepared, which table is searched for determining whether any value contained therein coincides with the outputs of the individual sensors, whereon the value for which the coincidence is found is read out from the table to be subsequently checked whether that value exceeds a predetermined value, in dependence on which the fire decision is then made.
The methods enumerated above suffer from the shortcomings mentioned below.
(a) Method based on the integration or multiplication of individual sensor outputs:
Although the principle underlying this method is plain, it is too simple for dealing with fire phenomena and lacks reliability to a disadvantage.
(b) Method using functions:
For monitoring all the fire phenomena inclusive of incipient or smoldering fires to conflagrations, a plurality of functions have to be employed, since a single function is insufficient. In that case, the functions must be exchanged in response to the output of a certain one of the sensors, which means that the finally obtained output becomes discontinuous. Further, because the output of the function can represent no more than one result, a number of functions corresponding to the number of possible results are required such as, for example, the probability of a fire and degree or level of danger. Also, great difficulty will be encountered in quickly obtaining a desired function when definitions of the input and output are to be altered or added to.
(c) Table method:
Since the input values from the individual sensors and the results are defined by employing a ROM or the like, there may arise such problems that when only some of the sensor outputs can fulfill the input conditions, blanks in the definition table have to be interpolated by resorting to a partial pattern matching method, although such interpolation is naturally unnecessary when all the input conditions are met. The interpolation becomes very complicated when the number of sensor inputs is great. Also, the table per se must be defined accurately and elaborately.